When firing a gas-operated or gas-assisted firearm, the backpressure generated by the propellant gases as the bullet traverses the bore is used to automatically cycle the operating group of the weapon. When firing low impulse ammunition such as blank cartridges, it is often necessary to use a Blank Firing Attachment (BFA) to generate sufficient backpressure to cycle the weapon. The BFA typically attaches to the muzzle end of the weapon's barrel.
The prior art BFA's used by the United States Army on gas-operated rifles and small and medium caliber machine guns utilize a cylindrical threaded stem and a housing that attaches to the weapon's muzzle compensator or flash suppressor. The threaded stem traverses axially during installation until the lower portion of the stem contacts either an internal feature of the muzzle device, a crush that sits between the muzzle device and barrel crown, or the barrel crown itself, at which point the bore is sealed. To prevent overpressure in the bore during firing, excess gas is released into the atmosphere through a bleed hole leading from an axial cavity in the BFA stem. Despite its use on the M4/M16 rifles, M249 Squad Automatic Weapon, and M240 Machine Gun, this style BFA does have several shortcomings.
Until now, the BFA design used by the U.S. Army is the subject matter of U.S. Pat. No. 5,325,758, entitled “Blank Firing Attachment” issued on Jul. 5, 1994 to Compton et al. (hereinafter “Compton”). Compton recognized that the threaded stem, exposed to corrosive gases when firing blanks, and stated that it must be manufactured of a material to withstand such gases, specifically, specifying ASTM A331 Grade 4140 cold finished steel.
Prior U.S. Pat. No. 3,766,822, entitled Blank Firing Adaptor for Gas Operated Firearms, issued Oct. 23, 1973 to Sophinos, disclosed an adaptor substantively identical in overall design to that disclosed herein; which uses a plug in place of the threaded stem disclosed by Compton. Sophinos, like Compton, merely states that the plug should be formed of a suitable heat resistant, rugged, fragible material such as steel. Such steel threaded stems or plugs, used by Compton, Sophinos, and the prior art, quickly erodes due to the corrosive gases after firing only a finite number of such rounds, often, as few as 200 rounds. This erosion of the threaded stem, or plug, allows excessive escape of propellant gases generated by the firing of the blank cartridge and therefore there is insufficient back-pressure to automatically cycle the operating group of the gas-operated weapon. Therefore, there is a need in the art for a BFA which will allow firing at least an order of magnitude more rounds, before failing.